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Old 14th October 2012, 04:27 PM   #271
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I saw the curve. The peak is big, but since the peak is not a resonance, EQ should fix it perfectly.
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Old 14th October 2012, 04:59 PM   #272
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Yes I can fix the peak (it is a resonance ? no? the load/mass of air in front and back of the drivers is visco-elastic ? ) but it is difficult to fix the phase/group delay.
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Old 15th October 2012, 01:36 AM   #273
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The RAAL dipoles just turned up... talk about a piece of art... cant wait to hear them.
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Old 15th October 2012, 06:55 AM   #274
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Quote:
Originally Posted by jerome69 View Post
Yes I can fix the peak (it is a resonance ? no? the load/mass of air in front and back of the drivers is visco-elastic ? ) but it is difficult to fix the phase/group delay.
No, its not really a resonance. The peak is caused by the front and rear radiation summing in-phase.

Have you measured the phase and group delay?
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Old 15th October 2012, 11:09 AM   #275
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Got home and did a bit of a mod to the test baffle. I moved the top 12MU to below the 2nd 12MU (making the 2nd 12MU the top). I then put the new RAAL dipole partially into the old top hole. Which now makes the tweeter a little closer to ear height.

Here are a couple of pics of the new dipole and the moded baffle. Yet to do any real testing but very first impressions are promising.
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Old 15th October 2012, 06:40 PM   #276
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Quote:
Originally Posted by StigErik View Post
No, its not really a resonance. The peak is caused by the front and rear radiation summing in-phase.

Have you measured the phase and group delay?
Yes I understand. But it looks a 1/4 wavelength resonance. Imagine the 1/2 x (2xU) tube as a pipe ... It looks like a transmission line ?

And Yes I made measurement and I have the SPL response, phase and group delay. But honestly I didn't need measurements to hear the problem.

To return to the original thread : It is big the dipole tweeter it sounds good ?
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Old 15th October 2012, 07:36 PM   #277
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The dipole peak expressed by the math formula is indeed impossible to work with but lets not forget that it is an extreme case modeled for circular baffles.

In practice things like the baffle size and shape as well as the position of the driver can help smooth out the dipole peak. It's worth spending a few minutes with the Edge baffle simulator to gain some perspective on the issue. In some configurations the dipole peak is severe but in others is quite usable.

I have no hard evidence but I even speculate that some drivers have more usable dipole peak at certain frequencies due to their mechanical construction. Parameters such as the magnet shape and the cone profile can affect the dipole characteristics.
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Old 15th October 2012, 07:39 PM   #278
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The "worst" example I've seen myself is an 11 dB tall dipole peak right in the midrange at 650 Hz. But it was successfully equalized with no audible trace of the peak....
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Old 15th October 2012, 11:02 PM   #279
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Originally Posted by jerome69 View Post
To return to the original thread : It is big the dipole tweeter it sounds good ?
Really not sure what to make of it at the moment. I seem to have inherited some contradictory traits…

The speaker seems more directional now than before, but at the same time sounds more open. I was just wondering if it now sounds more directional because I moved the top 12MU and the blending of the drivers is causing it to sound more source specific.

The other thing I noticed is that it really doesn’t seem to make any difference where I cross the tweeter / mids over.

With the monopole tweeter it made a huge difference when mounted on the baffle. Now I can cross over anywhere from 2000Hz to 4000Hz and can barely pick an audible difference.

I do have a theory about this that I need to try out… I think because the dipole tweeter is 2dB less sensitive than the monopole, I think the sound of the mids is drowning out the tweeter and is why I can’t pick it crossing over.
I don’t like the new sound all that much, but I don’t think it is the tweeter that is too blame, I think it is a result of putting the drivers too close together.

When mounted on a ” (19mm) MDF board the front and back faces are fairly flush. What I did find interesting is that the dipole tweeter uses the same aluminium element to radiate in both directions, same as a regular driver (I was expecting two elements for some strange reason, which makes no sense).
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Old 16th October 2012, 12:06 AM   #280
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Originally Posted by Silent Screamer View Post
Really not sure what to make of it at the moment. I seem to have inherited some contradictory traits…

I don’t like the new sound all that much, but I don’t think it is the tweeter that is too blame, I think it is a result of putting the drivers too close together.
You can't get them too close together. Technically, the closer the better for intergration at the crossover point. This should not be the problem. Have you measured anything yet?
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